1. Field of the Invention
The present invention relates to a microscopic geometry measuring device. More specifically, it relates to a microscopic geometry measuring device for accurately measuring a surface profile of LSI (large scale integration) and other semiconductor wafers.
2. Description of the Related Art
Conventionally, in accurately measuring the surface profile of a LSI and other semiconductor wafer, it is strongly desired to maintain a measuring force applied between a workpiece and a stylus in contact with the surface of the workpiece below a predetermined level. This is because damage to the workpiece and to the stylus can be prevented and the surface profile of the workpiece can be accurately reflected on the movement of the stylus by keeping the measuring force below a predetermined level. In order to meet the demand, a specially designed measuring device provided with a mechanism for controlling the measuring force below a predetermined level is used in accurately measuring the surface profile of semiconductor wafers.
The Applicant of the present application has proposed a measuring device disclosed in Japanese Patent Laid-Open Publication No. Hei 10-356187 as a conventional example of such measuring device. In FIG. 6, the measuring device 100 has a pivotable arm 101, a stylus mechanism 103 having a stylus 102 provided on a lower surface of an end of the arm 101 to be in contact with a workpiece, a measuring force adjusting mechanism 104 for adjusting a measuring force applied to the stylus 102, a displacement sensor 105 for detecting the position of the arm 101, and a measuring force control circuit 106 for controlling the measuring force adjusting mechanism 104. Here, reference numeral 101 A represents a pivot fulcrum of the arm 101 and 101B represents a balance weight provided on the other end of the arm 101. Displacements are recorded by computer 108.
The Applicant has also proposed a stylus mechanism disclosed in Japanese Patent Application No. Hei 11-272451 as the stylus mechanism 103 used in the measuring device 100.
The stylus mechanism 103 has a holder 103A to be attached to the arm 101, a stylus 102 held on the holder 103A and having a contact portion 102A to be in contact with the workpiece at the distal end thereof, a vibrator for resonantly vibrating the stylus 102 in an axial direction thereof, and a sensor for detecting a change in the resonance caused when the contact portion 102A touches the workpiece.
The measuring force adjusting mechanism 104 is composed of a magnetic substance 104A fixed on an upper side of the arm 101 and an electromagnetic actuator having an electromagnet 104B disposed right above the magnetic substance 104A. When the electromagnet 104B is electrified, a repulsive or attractive force is caused between the magnetic substance 104A and the electromagnet 104B to move the arm 101 vertically, so that the stylus 102 provided on one end of the arm 101 vertically displaces. A distance between the surface of the workpiece and the one end of the arm 101 is controlled by controlling the electrical current to the electromagnet 104B, thus keeping the measuring force applied between the stylus 102 and the workpiece below a predetermined level.
While the stylus 102 of the measuring device 100 is brought into contact with the surface of the workpiece, the stylus 102 is moved along the surface when measuring the workpiece. When the contact portion 102A of the stylus 102 touches the surface of the workpiece, the output signal from the sensor changes in accordance with vibration change of the stylus 102. The output signal is detected by a detecting circuit 107. The measuring force control circuit 106 controls the measuring force adjusting mechanism 104 (electromagnetic actuator) based on information from the detecting circuit 107, thus controlling the measuring force applied between the workpiece and the stylus 102.
The measuring device 100 controls the movement of the arm 101, i.e. the movement of the contact portion 102A of the stylus 102 with a single electromagnetic actuator (the measuring force adjusting mechanism 104). In order to move the contact portion 102A to follow the workpiece surface while applying the predetermined level of measuring force, the contact portion 102A has to be moved in a direction perpendicular to the workpiece surface in an order ranging from a nanometer to a millimeter.
However, there is 106 divergence between the nanometer and the millimeter order. When the movement of the contact portion 102A is controlled with the above range by the single electromagnetic actuator, supposing the minimum value of the electromagnetic actuator is controlled at 1 mV (i.e., controlling 1*10xe2x88x926 mm at 1 mV), the maximum value has to be controlled at 1000 V (i.e. controlling 1 mm at 1000 V). Since the control value range is too wide, the measuring force control has been difficult.
An object of the present invention is to provide a microscopic geometry measuring device capable of easily and accurately controlling the movement of the stylus from nanometer to millimeter order so that the stylus accurately follows the workpiece surface at a predetermined measuring force, thus reducing damage on the workpiece and the stylus and improving the measurement accuracy.
The inventors has contemplated combining two mechanisms, i.e. a fine feed mechanism for displacing the stylus within a range from a nanometer order to a micrometer order, and a coarse feed mechanism for displacing the stylus from a micrometer order to a millimeter order, to move the stylus within the range from the nanometer order to the millimeter order. For instance, a piezoelectric element (PZT) may be utilized as the fine feed mechanism, and an electromagnetic actuator may be utilized for the coarse feed mechanism, both of which can be constructed using a known technique. The combination of the known fine feed mechanism and the coarse feed mechanism may be conducted, for instance, by providing the stylus on a movable portion of the fine feed mechanism and providing a fixed portion of the fine feed mechanism to a movable portion of the coarse feed mechanism.
However, when the fine feed mechanism and the coarse feed mechanism are simply combined, the reaction force caused by the movement of the movable portion of the fine feed mechanism influences the fixed portion of the fine feed mechanism to apply force to the movable portion of the coarse feed mechanism provided with the fixed portion. In other words, a mechanical interference is caused between the fine feed mechanism and the coarse feed mechanism. When the mechanical interference is caused between the fine feed mechanism and the coarse feed mechanism, the stylus displaces in a complicated and uncontrollable manner, so that the measuring force cannot be controlled by an accurate control of the stylus movement. Uncontrollable measuring force applied to the stylus results in deterioration in measurement accuracy and, possibly, damage on the workpiece and the stylus.
In order to eliminate the mechanical interference between the fine feed mechanism and the coarse feed mechanism, the mass of the fixed portion of the fine feed mechanism may be set sufficiently greater than the mass of the movable portion, so that the reaction force of the movable portion is absorbed by the fixed portion to block the force applied from the fine feed mechanism to the coarse feed mechanism. However, in this case, since the mass of the entire fine feed mechanism is increased and the mass applied on the movable portion of the coarse feed mechanism for the fine feed mechanism to be provided is increased, the responsivity of the coarse feed mechanism is lowered, so that the measurement speed cannot be increased.
In order to eliminate mutual interference between the fine feed mechanism and the coarse feed mechanism without greatly increasing the mass of the movable portion of the coarse feed mechanism, a microscopic geometry measuring device according to the present invention has following arrangement.
According to an aspect of the present invention, a microscopic geometry measuring device has: a stylus to be in contact with a workpiece; a quantity of state sensor for quantitatively detecting a state which changes when the stylus is in contact with the workpiece; a drive mechanism for relatively moving the stylus and the workpiece in a direction substantially perpendicular to the surface of the workpiece; a displacement sensor for detecting a relative movement of the stylus and the workpiece by the drive mechanism; and a measuring force control circuit for adjusting a measuring force applied to the stylus, where the drive mechanism has a fine feed mechanism having a fixed portion and a movable driving portion displacing relative to the fixed portion for minutely displacing the stylus and/or the workpiece and a coarse feed mechanism having a movable portion attached to the fixed portion of the fine feed mechanism for displacing the stylus and/or the workpiece, the fine feed mechanism having a movable balancing portion structured approximately identical with the movable driving portion of the fine feed mechanism to be moved in a direction opposite to a movement direction of the movable driving portion. The measuring force control circuit actuates at least one of the fine feed mechanism and the coarse feed mechanism based on an output signal from the state sensor to adjust the measuring force applied to the stylus.
The microscopic geometry measuring device has two mechanisms, i.e. the fine feed mechanism for minutely displacing the stylus within a range, for instance, from nanometer order to micrometer order and the coarse feed mechanism for greatly displacing the stylus within a range from micrometer order to the millimeter order. In order to drive the stylus within a range of the nanometer order to the micrometer order, the fine feed mechanism is actuated. In order to drive the stylus within a range of micrometer order to millimeter order, the coarse feed mechanism is actuated. By combining the actuation of the fine feed mechanism and the coarse feed mechanism, the movement of the stylus can be easily controlled within a range from the nanometer order to the millimeter order at a short time.
Further, since the fine feed mechanism has a movable balancing portion having approximately the same structure as the movable driving portion of the fine feed mechanism being driven in a direction opposite to the driving direction of the movable driving portion, the reaction force to the fixed portion in actuating the movable driving portion is cancelled at the fixed portion of the fine feed mechanism by the reaction force applied to the fixed portion generated by actuating the movable balancing portion (a force opposite to the reaction force generated by actuating the movable driving portion). In other words, the reaction force by the movable driving portion of the fine feed mechanism does not influence on the movable portion of the coarse feed mechanism. Accordingly, since there is no mechanical interference between the fine feed mechanism and the coarse feed mechanism, the stylus does not complicatedly or uncontrollably displace, thus accurately controlling the movement of the stylus with the fine feed mechanism and the coarse feed mechanism. Therefore, the measuring force applied to the stylus can be accurately controlled to reduce damage on the workpiece and the stylus while improving measurement accuracy.
In the above arrangement, the stylus may preferably resonantly vibrate in an axial direction thereof, and the quantity of state sensor may preferably detect the vibration of the stylus.
Generally, since the flexural natural frequency in the axial direction is lower than the natural frequency in the axial direction, the stylus vibrating in the axial direction has higher responsivity than a stylus with flexural vibration in the axial direction. Accordingly, the measuring force applied to the stylus can be more accurately controlled by detecting the vibration as a quantity of state of the highly-responsive stylus with the detector, the vibration changing when the stylus touches the workpiece, so that the fine feed mechanism and the coarse feed mechanism are actuated based on the information from the detector.
In the above aspect of the present invention, the movement direction of the fine feed mechanism and the coarse feed mechanism may preferably be along an axial direction of the stylus.
Accordingly, since the moving direction of the fine feed mechanism and the coarse feed mechanism are along the axial direction of the stylus, the stylus can be moved while the axial direction of the stylus is along the height direction of the surface of the workpiece. In other words, since the stylus can be securely pressed against the surface of the workpiece along the axial direction thereof, the change in vibration of the stylus resonantly vibrating along the axial direction thereof can be more accurately detected by the detector.
In the above aspect of the present invention, the stylus may preferably be longitudinally approximately orthogonal with a movement direction of the fine feed mechanism and the coarse feed mechanism and may preferably be provided to the fine feed mechanism through an elastic lever elastically deformable in a direction along the movement direction, the quantity of state sensor detecting an elastic deformation of the elastic lever.
Accordingly, the elastic lever elastically deforms by virtue of the measuring force applied to the stylus. The measuring force can be controlled by actuating the fine feed mechanism and the coarse feed mechanism based on the elastic deformation of the elastic lever.
In the above aspect of the present invention, the fine feed mechanism may preferably include a high-speed minute displacement solid element such as a piezoelectric element and a magnetostrictor.
Accordingly, by laminating thin plates of PZT (lead zirconate titanate) having electrostrictive effect to construct the piezoelectric element, the electrically controllable fine feed mechanism can be easily constructed. The high-speed minute displacement solid element may be magnetostrictor and shape memory alloy as well as the piezoelectric element such as PZT.
In the above aspect of the present invention, the coarse feed mechanism may preferably include: a fixed portion; a movable portion movable in a height direction of the surface of the workpiece relative to the fixed portion; and a parallel pair of arm spaced apart in height direction of the surface of the workpiece, the pair of arm having one end rotatably secured to the fixed portion and the other end rotatably secured to the movable portion.
Since the movable portion is held on the parallel pair of arm vertically spaced apart relative to the fixed portion, the movable portion can be vertically moved without changing attitude thereof. Accordingly, when the stylus is provided to the movable portion, the stylus can be moved without changing the attitude of the stylus.
Further, since the arm is provided to the fixed portion and the movable portion through the elastic hinge without requiring lubricant oil, the coarse feed mechanism can be kept clean and is effective for measuring surface profile of a semiconductor wafer.
Further, since the rotary movement of the arm by virtue of the elastic hinge has smaller friction than a rotary movement of the arm using a rolling bearing etc., the movable portion can be accurately moved in parallel without slack.
In another aspect of the present invention, the coarse feed mechanism may preferably include an air bearing or an elastic plate spring.
Since the coarse feed mechanism uses an air bearing or an elastic plate spring without requiring lubricant oil, the coarse feed mechanism can be kept clean, thus being suitable for measuring surface profile of semiconductor wafer.
In a further aspect of the present invention, the displacement sensor may preferably include a fist displacement sensor for detecting a relative movement between the stylus and the workpiece caused by the fine feed mechanism and a second displacement sensor for detecting a relative movement between the stylus and the workpiece caused by the coarse feed mechanism.
Since the microscopic geometry measuring device has the first displacement sensor for detecting the movement of the stylus by the fine feed mechanism and the second displacement sensor for detecting the movement of the stylus by the coarse feed mechanism, the displacements of the stylus by the fine feed mechanism and the coarse feed mechanism can be detected independently, thus facilitating independent control of the fine feed mechanism and the coarse feed mechanism.
In further aspect of the present invention, the displacement sensor may preferably detect a relative movement between the stylus and the workpiece caused by the fine feed mechanism and the coarse feed mechanism.
Since the displacement sensor for detecting the movement of the stylus by the fine feed mechanism and the coarse feed mechanism is composed as a single component, the cost can be reduced.